GRANT=6673577;P20RR Many psychiatric disorders, including drug abuse, are characterized by behavior that is deemed "impulsive." Impulsivity is often defined as the choice for a small, immediate outcome or reinforcer over a larger, more delayed outcome, the self-controlled choice. Impulsive choices may be a result of the value of the larger reinforcer being discounted due to the delay to its presentation. Drug abusers have been shown to discount the value of delayed outcomes to a greater extent than non-drug abusers. However, it is not clear whether delay discounting and/or impulsive choice is an acute drug effect, a consequence of long-term drug exposure, or a pre-existing component of an individual's behavioral repertoire determined by behavioral history and/or genetics. The present proposal is designed to begin to address these issues by the investigation of acute and chronic effects of drugs of abuse on impulsive choice in an animal model using two different rat strains, Lewis and Fischer 344, that differ in potentially relevant neurochemical and behavioral measures. The research has three Specific Aims that are addressed in three series of experiments. Specific Aim 1 is to investigate acute effects of drugs of abuse on impulsive choice in the two rat strains, which are expected to differ in their impulsive choices. Specific Aim 2 is to examine effects of repeated administration (long-term exp0osure) of drugs of abuse on impulsive choice in the two rat stains. Specific Aim 3 will enable us to better understand issues surrounding neurochemical bases of impulsivity and drug effects on impulsive choice. Within this aim is included investigations effects of selective serotonin and dopamine receptor ligands on impulsive choice modified by drugs of abuse. Also included is examination of differential brain neurochemistry between the two rat strains and how any difference in neurochemistry is related to impulsive choice and drug effects on that choice. Differential and systematic findings in impulsive choice and drug effects will lay the foundation for further studies into understanding the role of neurochemistry and genetics into delay discounting and impulsive choice. The proposed research will contribute to the understanding of the neurobehavioral biology of delay discounting and impulsive choice and effects of drugs of abuse. Ultimately, this work may have relevance to, including understanding and treatment of, many psychiatric disorders characterized by impulsive behavior, e.g., drug abuse, gambling, violence, attention-deficit hyperactivity disorder (ADHD).